The present invention relates to a duct fan adapted to be arranged in a duct for transport of air between an upstream duct part and a downstream duct part according to the description herein.
Accordingly, duct fans are fans installed in ducts for transport of air for forcing air through these ducts and they are sometimes also called “in line centrifugal fans”. The ducts may be of any type in which it is a desire to transport air, such as ventilation ducts in any type of building, such as in dwelling houses, in industrial premises, in sports halls and the like, and air is here to be interpreted to include any gases or gas mixtures, such as air contaminated with any other gas, such as carbon monoxide.
Duct fans for transport of air in circular ducts were until now mostly so-called circular duct fans having an impeller with the axis of rotation substantially in parallel with the direction of the main transport of air from the inlet to the outlet of the fan and when installed between an upstream duct part and a downstream duct part by that substantially in parallel with the extension of that duct in that region. However, such circular duct fans require comparatively much space in the direction perpendicular to said axis of rotation of the impeller, which often means in the vertical direction, since the ducts in question are often extending directly under or in ceilings of buildings. This means a waste of space that may be utilised in a more efficient way.
Furthermore, the pressure that may be obtained through such a circular duct fan in a duct is not as high as desired, at the same time as the noise level is rather high.
Duct fans of the type defined in the description herein, i.e. having a radial impeller having the axis of rotation substantially perpendicular to the direction of the main transport of air from the inlet to the outlet, have for that sake been put on the market. Such duct fans may be constructed with smaller dimensions in the transversedirection thereof, i.e. in the direction substantially perpendicular to the direction of the main transport of air from the inlet to the outlet, which in the practice means a lower height and less space demand in that context. Although such a duct fan is preferred with respect to a circular duct fan also with respect to obtainable pressure, noise level and efficiency, there is a desire to further improve the properties thereof.